PREVENTIVE MEDICINE 315 



very least 22 weeks, made up as follows : egg-laying 1 week, 

 hatching out of larvae 6 weeks, moulting of larvae 4 weeks, nymphs 

 to adults 8 weeks, attachment of adult ticks 1 week, and to this 

 one must add the few days before larvae are capable of attaching 

 themselves and the few days' attachment of larvae and nymphs. 

 As a rule, the period will be longer than this owing to cold weather, 

 which has a slowing effect, and to the time (variable of course) 

 before the tick happens to find a host. 



The life-cycle of Hamaphysalis punctata is similar, but the 

 time occupied by the individual stages is somewhat longer. Stock- 

 man found that the minimum period during which all stages could 

 be passed was 94 days made up thus : egg laying 10 days, hatch- 

 ing 38 days, larvae resting 3 days, larvae engorged in 5 days, larva 1 

 moulted in 14 days, nymphs resting for 3 days, nymphs engorged 

 in 4 days, nymphs moulted in 7 days, adults resting for 4 days, 

 adults engorged in 6 days. The usual cycle probably lasts about 

 160 days, and there is as a rule only one generation per annum. 

 Hatching of eggs mostly occurs in July and, to a less extent, in 

 August ; moulting of larvae to nymphs mostly takes place in August 

 and September and less in October, and many of the latter engorge 

 during the same months. A large proportion of nymphs moult 

 to adults from September onwards, and pass the winter thus, but 

 many do not become engorged or moult, as the case may be, until 

 the following spring or later. The latter supply the large number 

 of adults found to have become engorged in April and May. Lay- 

 ing of eggs chiefly occurs in May and June. Adults are thus 

 most numerous in spring and early summer and in autumn, or at 

 the times at which redwater is most prevalent. 



PREVENTIVE MEASURES. The prevention of bovine piroplas- 

 mosis may be partially effected by reducing the number of ticks, 

 and this can be done by cleaning and draining the land and 

 where possible tilling it, though in many districts and on many tick- 

 infected pastures it is impossible to convert the grazing into tillage. 

 Cleaning and draining, however, will do a lot to free the land from 

 ticks. A top dressing of lime or salt is also recommended, at the rate 

 of 3 tons of the former or a ton of the latter per acre. If it is 

 impracticable to thoroughly clean the land of ticks, this should be 

 done as well as may be and cattle should then be kept off such pas- 

 tures for two years. It is a positive advantage to graze sheep on red- 

 water land as ticks become cleansed of infection by feeding on sheep. 

 It must, however, be remembered that by returning " carrier " 

 cattle to purified ground one simply re-introduces the disease. If 

 it is impracticable to keep cattle off the pastures, one may at least 



